In an image display device such as a cathode ray tube display device (CRT), a plasma display device (PDP), an electroluminescence display (ELD) or a liquid crystal display device (LCD), an anti-reflection film is generally disposed over the outermost surface of the display device so as to reduce reflectance based on the principle of optical interference for the purpose of preventing reduction of contrast due to reflection of external light or reflection of undesired images in its screen.
Such anti-reflection film can generally be prepared by forming a low refractive index layer having an appropriate thickness on a support or on a high refractive index layer formed thereon. In view of anti-reflection performance, a material having a refractive index as low as possible is desired as the material for the low refractive index layer and, at the same time, the material is required to have high stain-proof properties and high scratching resistance since the anti-reflection film is used over the outermost surface of the display. In order to obtain high scratching resistance with respect to a thin film of about 100 nm in thickness, it is of importance to enhance strength of the film itself.
As a polymer for forming the low refractive index layer, it is well known to cure a fluorine-containing polymer having a low refractive index and use the cured polymer. Also, regarding the curing method, there have been known various methods. For example, it has been commonly conducted to cure a polymer having hydroxyl group with various curing agents (JP-A-57-34107, JP-A-61-275311 and JP-A-8-92323). However, such conventional polymers are still insufficient with respect to film hardness, and have been required to be improved.
As a means to reduce the refractive index of a material, there is a method (2) of reducing the density of the material (introducing voids into the material) in addition to the method (1) of introducing fluorine atom into the material. However, both methods involve the problem that film strength is impaired and scratching resistance is reduced.
As a method of markedly improving stain-proof properties and scratching resistance while keeping the refractive index at a low level, it is effective to impart slipping properties to the surface. With respect to imparting slipping properties to the surface, techniques of introducing fluorine and introducing silicon are effective. In particular, addition of a small amount of a silicone series compound to a low refractive index material provides markedly improved surface slipping properties, markedly improved stain-proof properties and markedly improved scratching resistance. On the other hand, however, there have been involved various problems such as poor compatibility with materials in a low refractive index layer, bleed-out with the elapse of time or under the condition of high temperature, transfer of the silicone component to a medium in contact therewith, and deterioration of performance and stain of the production line due to these phenomena.
Particularly with an anti-reflection film, generation of haze due to the insufficient compatibility deteriorates optical performance, thus being a serious problem. Also, upon winding up a film after coating thereon the low refractive index layer, the silicone series compound can adhere to the back side of the film, which causes troubles in the successive processing steps, thus such adhesion having been a serious problem. That is, there has been required a technique of effectively precipitating only a siloxane moiety of the compound on the surface and allowing the remaining moiety of the compound bound to silicon atom to effectively anchor into the film of the low refractive index layer.
Regarding this problem, there have been proposed techniques (JP-A-11-189621, JP-A-11-228631, JP-A-2000-17028 and JP-A-2000-313709) of fluorine-containing olefin copolymers into which a polysiloxane block copolymer component is introduced using a silicone series macroazo initiator and applying the copolymer to the use of an anti-reflection film.